1. Field of the Invention
The present invention relates to rotating shafts generally and, more particularly, but not by way of limitation, to a novel sensor arrangement for sensing angular velocity, torque, and power.
2. Background Art
While the present invention is described primarily, for illustrative purposes only, as being applied to bicycle-type devices, it will be understood that it can be applied as well to sensing torque of any shaft, such as shafts on motors, medical monitoring equipment, and other exercise devices.
Torque responsive throttles have been of interest for power-assisted bicycles to provide motor power to the bicycle when the power exerted by the bicycle operator reaches a predetermined level. It has been reported that, in at Least one country, there is a requirement, in order to conserve fuel, that power-assist be applied only after a predetermined velocity is reached and auxiliary motor power is provided only up to the power provided by the cyclist. A primary measurement of power level can be derived from a measurement of torque on, and angular velocity of, the shaft extending between the two crank arms of the bicycle and the sprocket drive. Alternatively, the measurement can be made of only one crank and the values doubled.
A number of techniques can be employed to provide devices to measure the torsion of shafts, which torsion is proportional to torque. Some of these techniques suffer from the disadvantages of complexity and, therefore, relatively high cost and weight, some require slip rings with the attendant problems, some cannot be packaged for use in a bicycle environment, some are unsuitable for use in a bicycle environment where the device is subject to exposure to liquids and foreign solid materials, such as water, ice, salts, dirt. grime, etc., and none provides a simple technique for protecting the shaft from excess torque and excess bending.
Accordingly, it is a principal object of the present invention to provide a shaft sensor assembly that is relatively simple and inexpensive.
It is a further object of the present invention to provide such a shaft sensor assembly that is suitable for use in a bicycle environment.
It is an additional object of the present invention to provide such a shaft sensor assembly that provides a simple technique for protecting the shaft from excess torque and excess bending.
It is another object of the present invention to provide such a shaft sensor assembly that is highly sensitive.
It is yet a further object of the present invention to provide such a shaft sensor assembly that provides an indication of angular velocity, torque, and power levels when the shaft is rotating, without the use of slip rings or telemetry methods.
It is yet an additional object of the invention to provide such a shaft sensor that can be easily and simply assembled.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description and the accompanying drawing figures.
The present invention achieves the above objects, among others, by providing, in a preferred embodiment, a shaft sensor for a machine, said shaft sensor comprising: first and second disks, fixedly orthogonally attached to a portion of a shaft of said machine, said portion of said shaft being subject to torsion, and said first and second disks being operatively attached to said portion of said shaft at spaced apart locations along said portion of said shaft; and a sensor assembly, including first and second sensors, disposed in sensing relationship with said first and second disks to sense relative position of said first and second disks resulting from torsion of said portion of said shaft and to output a signal representative of at least one parameter related to torsion of said shaft.
In another preferred embodiment, said shaft is discontinuous and said first and second disks are attached, respectively, to first and second portions of said shaft and have a resilient member disposed therebetween.